Method of manufacturing thin film transistor

ABSTRACT

A method of manufacturing a thin-film transistor is provided, including preparing ink including a solution in which a graphene oxide, a reduced graphene oxide, or a combination thereof is dispersed, forming the ink on a substrate in the form of a pattern, and forming a source electrode and a drain electrode that are positioned at edges of the pattern and a semiconductor channel positioned between the electrodes by a coffee-ring effect in the ink by using the graphene oxide, the reduced graphene oxide, or the combination thereof within the formed pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2013-0108576 filed in the Korean IntellectualProperty Office on Sep. 10, 2013, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method of manufacturing a thin filmtransistor.

(b) Description of the Related Art

In general, since various electronic devices such as a display device, alight-emitting diode, and a solar cell transmit light to form an imageor generate power, the electronic devices require a transparentconductive film capable of transmitting light. As the transparentconductive film, indium tin oxide (ITO) has been widely used.

However, as the consumption amount of indium is increased, economicefficiency of the indium tin oxide may be deteriorated due to high cost.Particularly, since the transparent conductive film including the indiumhas a chemical and electrical defect, a transparent conductive materialthat can replace the transparent conductive film is needed.

As such a transparent conductive material, graphene has attractedattention. The graphene is a material made of a honeycomb carbon latticehaving a one-atom thickness, and since the graphene has high electricalconductivity and transparency, the graphene has attracted attention asan important material that can be applied to various future devices suchas a semiconductor device, a solar cell, a supercapacitor, and aflexible display.

Accordingly, a method of effectively manufacturing and using graphene ora graphene oxide is needed, and studies on applying the graphene or thegraphene oxide to various electronic devices are also needed.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a method ofmanufacturing a single-process thin-film transistor.

An exemplary embodiment of the present invention provides a method ofmanufacturing a single-process thin-film transistor, including:preparing ink including a solution in which a graphene oxide, a reducedgraphene oxide, or a combination thereof is dispersed; forming the inkon a substrate in the form of a pattern; and forming a source electrodeand a drain electrode that are positioned at edges of the pattern and asemiconductor channel positioned between the electrodes by a coffee-ringeffect in the ink by using the graphene oxide, the reduced grapheneoxide, or the combination thereof within the formed pattern.

The method of manufacturing a single-process thin-film transistor mayfurther include reducing the graphene oxide within the formed sourceelectrode, drain electrode, and semiconductor channel after the forminga source electrode and a drain electrode that are positioned at edges ofthe pattern and a semiconductor channel positioned between theelectrodes by a coffee-ring effect in the ink by using the grapheneoxide, the reduced graphene oxide, or the combination thereof within theformed pattern.

In the reducing of the graphene oxide within the formed sourceelectrode, drain electrode, and semiconductor channel, intense pulsedlight may be used.

The method of manufacturing a single-process thin-film transistor mayfurther include separating and cutting the source electrode and thedrain electrode in the formed source electrode, drain electrode, andsemiconductor channel.

In the preparing ink including a solution in which the graphene oxide,the solution in which the graphene oxide, the reduced graphene oxide, orthe combination thereof is dispersed may include an organic solvent,water, or a combination thereof in which the graphene oxide, the reducedgraphene oxide, or the combination thereof is dispersed.

The solution in which the graphene oxide, the reduced graphene oxide, orthe combination thereof is dispersed may include 0.01 wt % to 3 wt % ofgraphene oxides, the reduced graphene oxide, or the combination thereof.

The organic solvent may be n-methyl pyrrolidone (NMP),dimethylpyrrolidone, ethylene glycol, acetone, tetrahydrofuran,acetonitrile, dimethylformamide, methanol, ethanol, propanol, dimethylsulfoxide, chloroform, cyclopentanone, or a combination thereof.

The organic solvent, the water, or the combination thereof may include afirst solvent and a second solvent, and the second solvent may havelower viscosity and surface tension than those of the first solvent, ormay have higher viscosity and surface tension than those of the same.

In the forming of the ink on a substrate in the form of a pattern, a tomethod of selectively controlling wettability of the solution, an inkjetprinting method, or a method using a dispenser may be used.

In the inkjet printing method, a volume of discharged ink may be 1 μl orless.

In the forming of a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof within the formed pattern, the formed source electrode and drainelectrode may have a thickness of 5 nm to 50 nm, and the formedsemiconductor channel may have a thickness of 10 nm or less.

A difference between the thickness of source electrode and drainelectrode and the thickness of the semiconductor channel may be 2 nm ormore.

A distance between the source electrode and the drain electrode may be20 μm to 200 μm.

The method of manufacturing a single-process thin-film transistor mayfurther include removing a remaining solvent in the ink after theforming of a source electrode and a drain electrode that are positionedat edges of the pattern and a semiconductor channel positioned betweenthe electrodes by a coffee-ring effect in the ink by using the grapheneoxide, the reduced graphene oxide, or the combination thereof within theformed pattern.

The intense pulsed light may have a pulse duration of 1 msec to 500msec.

The intense pulsed light may have a pulse-off time of 0.1 msec to 500msec.

The intense pulsed light may have energy of 5 J/cm² to 200 J/cm².

The substrate may include silicon, glass, an oxide, a nitride, aplastic, or a combination thereof.

In the inkjet printing method, a discharging rate may be 100 μm/s to 200μm/s.

In the inkjet printing method, a discharge volume may be 1 μL or less, adischarging rate may be 1 Hz to 1000 Hz, and a temperature of thesubstrate may be 25° C. to 90° C.

The forming of a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide or the combinationthereof within the formed pattern may include increasing the coffee-ringeffect by heating the substrate on which the pattern is formed toimprove an evaporating rate of the solvent from the ink.

In the method of selectively controlling wettability of the solution,the pattern may be formed by allowing the ink to soak into the patternin which the surface energy is controlled, as a result of selectivelycontrolling surface energy on the substrate in a regular pattern form.

According to an embodiment of the present invention, it is possible toprovide a method of manufacturing a thin-film transistor capable ofreducing cost, processing time, and occupying space by simplifying aprocess. More specifically, a photolithography process and a maskprocess may not be performed.

Further, the manufacturing method is an environmentally-friendlyprocess, and may not use a photoresist or an etching solution.

Furthermore, efficiency of a material is excellent, unlike an existingspin coating method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram for describing a method of manufacturing athin-film transistor according to an exemplary example of the presentinvention.

FIG. 2 illustrates a single-process graphene transistor using acoffee-ring effect.

FIG. 3 illustrates XPS analysis results of C1s before and afterprocessing a graphene oxide coffee-ring pattern according to Example 1with intense pulsed light.

FIG. 4 is a graph illustrating electric field effect mobility of thegraphene oxide single-process transistor according to Example 1depending on processing conditions of the intense pulsed light.

FIG. 5 is a graph exhibiting an output characteristic (IDS-VDS) of thethin-film transistor according to Example 1.

FIG. 6 is a graph exhibiting transfer characteristic (IDS-VGS)performance of the thin-film transistor manufactured according toExample 1.

FIG. 7 is a graph exhibiting a transfer characteristic (IDS-VGS) and theinside of the single-process graphene transistor using an inkjetprinting method according to Example 1.

FIG. 8 illustrates a single-process transistor of a reduced grapheneoxide (RGO) using a coffee-ring effect according to Example 2.

FIG. 9 is a graph exhibiting a current characteristic (I_(DS)-V_(DS)) ofthe thin-film transistor manufactured according to Example 2.

FIG. 10 is a graph exhibiting transfer characteristic (IDS-VGS)performance of the thin-film transistor manufactured according toExample 2.

FIG. 11 illustrates photographs of various types of patterns other thana line pattern, which are formed through a method of selectivelycontrolling wettability, and data obtained by analyzing thicknessesthereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will hereinafter bedescribed in detail, and may be easily performed by those who areskilled in the related art. However, the present invention may bemodified in various different ways, and it is not limited to theexemplary examples described herein.

In the drawings, the thickness of layers, films, panels, regions, etc.,are exaggerated for clarity. Like reference numerals designate likeelements throughout the specification. It will be understood that whenan element such as a layer, film, region, or substrate is referred to asbeing “on” another element, it can be directly on the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly on” another element, there are nointervening elements present.

Hereinafter, a method of manufacturing a thin-film transistor accordingto an exemplary example of the present invention will be described withreference to the drawings.

An exemplary embodiment of the present invention provides a method ofmanufacturing a single-process thin-film transistor including: preparingink including a solution in which a graphene oxide, a reduced grapheneoxide, or a combination thereof is dispersed; forming the ink bydischarging it on a substrate in the form of a pattern using an inkjetprinting method; and forming a source electrode and a drain electrodethat are positioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof within the formed pattern.

Further, the method of manufacturing a single-process thin-filmtransistor may further include reducing the graphene oxide within theformed source electrode, drain electrode, and semiconductor channelafter the forming of a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof within the formed pattern.

In the reducing the graphene oxide within the formed source electrode,drain electrode, and semiconductor channel, an intense pulsed light maybe used. However, the present invention is not limited to the method.

Furthermore, the method of manufacturing a single-process thin-filmtransistor may further include separating and cutting the sourceelectrode and the drain electrode in the formed source electrode, drainelectrode, and semiconductor channel.

Such a method can be easily performed with a printing process or apattern forming process, and can effectively obtain a desired channelwidth or shape.

For more specific description, a schematic diagram for describing amethod of manufacturing a thin-film transistor according to an exemplaryexample of the present invention is illustrated in FIG. 1.

The method of manufacturing a thin-film transistor according to theexemplary example of the present invention can effectively manufacture athin-film transistor by a single process by maximizing a coffee-ringeffect caused by a print pattern process and an electricalcharacteristic of the reduced graphene oxide.

FIG. 1 schematically illustrates the coffee-ring effect.

The coffee-ring effect refers to a phenomenon in which fluid flow inwhich a solvent of the solution produced in a regular pattern byprinting or various methods flows from a center of the solution towardan edge thereof due to a non-uniform evaporation rate of the solvent ona surface of the solution occurs, and thus a solute in the solution isthickly layered at an edge of a solution droplet to be formed in a ringshape.

Such a phenomenon is generally observed when a solution having lowviscosity quickly evaporates on the substrate, and a distribution of thesolute can be controlled by the coffee-ring effect by adjusting flow ofthe solvent. Particularly, the flow of the solvent can be adjusted usingthe evaporation rate of the solvent, wettability for the substrate, anda mixed solvent.

The graphene is a material made of a honeycomb carbon lattice having anone-atom thickness, and since the graphene has high electricalconductivity and an excellent physical property, the graphene has gainedattention as an important material that can be applied to various futuredevices such as a high performance semiconductor device, a solar cell, asupercapacitor, a flexible display, a memory, a computer componenthaving a thin-paper shape, and a nano-bio material. Since single-layergraphene has very high transparency of 97% or more and high mechanicalstrength, a performance loss thereof due to deformation is lessincurred, and thus the graphene is highly likely to be applied to aflexible device in the future.

In order to replace the graphene having a difficulty in a solutionprocess, the reduced graphene oxide may be used. The reduced grapheneoxide may be manufactured by reducing the graphene oxide. Since thegraphene oxide can be easily dispersed in water, the graphene oxide isappropriate for the solution process.

When the reduced graphene oxide is used, it is possible to manufacture aconductive thin film having mechanical stability and high transparency.However, since it is difficult to perfectly reduce the graphene oxideduring the graphene oxide reducing process, the graphene oxide has lowerconductivity and charge mobility than graphene manufactured by generalgrowth.

Moreover, the reduced graphene oxide may have a semiconductorcharacteristic in which metallicity of high conductivity is changed byan electric field depending on a thickness of the thin film and a degreeof reduction of the graphene oxide. When the thickness of the thin filmis small (for example, less than 10 layers), a semiconductorcharacteristic in which symmetry of electrical interaction of carbonatoms is collapsed (A-B stacking) and is changed by the electric fieldis observed. In addition, when the thickness is large (for example, 10layers or more), an electrical property of metallicity is observed dueto high conductivity.

Since the method of manufacturing a thin-film transistor according tothe exemplary example of the present invention is a single process inwhich the transistor is manufactured through the solution processing byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof, and the graphene oxide is selectively reduced, it is possibleto decrease a process time, an occupying space, and cost by simplifyingthe process. More specifically, an existing photolithography process anda mask process may not be performed. When the transistor is manufacturedusing only the reduced graphene oxide, the reducing process may also notbe performed, so that it is possible to simplify the process.

Accordingly, since a photoresist and an etching solution are not used,it is possible to perform an environmentally-friendly process. Unlike aspin coating method that is mostly used, it is possible to improveefficiency of the material.

Further, when the graphene oxide is reduced using the intense pulsedlight, it is possible to control a degree of reduction of the grapheneoxide, and it is possible to manufacture the transistor withoutaffecting an interface.

More specifically, in the prepared ink including a solution in which thegraphene oxide, the reduced graphene oxide, or the combination thereofis dispersed, the ink solution may include an organic solvent, water,and a combination thereof in which the graphene oxide, the reducedgraphene oxide, or the combination thereof is dispersed.

The organic solvent may be n-methyl pyrrolidone (NMP),dimethylpyrrolidone, ethylene glycol, acetone, tetrahydrofuran,acetonitrile, dimethylformamide, methanol, ethanol, propanol, dimethylsulfoxide, chloroform, cyclopentanone, or a combination thereof.

In general, when a single solvent (for example water) is used, if anevaporation rate of the solvent is high, it is possible to maximize thecoffee-ring effect. A solvent having low viscosity and high volatilitymay be used in order to maximize the coffee-ring effect, or thesubstrate may be heated in order to increase the evaporation rate of thesolvent. Further, it is possible to obtain the same effect by improvingwettability for the substrate.

As an example of the ink, ink in which the reduced graphene oxide isdispersed in the n-methyl pyrrolidone (NMP) may include 0.01 wt % to 3wt % of reduced graphene oxides. More specifically, in this case, it ispossible to effectively exhibit the coffee-ring effect by heating thesubstrate to a temperature of 60° C. or more.

In addition, water in which the graphene oxide is dispersed may include0.01 wt % to 3 wt % of graphene oxides. In such a case, as aconcentration thereof is low, the coffee-ring effect can be increased.

When the coffee-ring effect is controlled using the mixed solvent, if asecond solvent having lower viscosity and surface tension than those ofa first solvent is added, or having higher viscosity and surface tensionthan those of the same, it is possible to maximize the coffee-ringeffect. This is a principle that controls flow of the solvent (Marangoniflow) induced due to a surface tension difference in the patternedsolution to be directed from the center of the liquid droplet toward theedge thereof.

More specifically, in the forming the ink on a substrate in the form ofa pattern, a method of selectively controlling wettability of thesolution, an inkjet printing method, or a patterning method using adispenser may be used. However, the present invention is not limited tothe above-stated methods.

As an example of the method of selectively controlling wettability ofthe solution, when a UV-ozone process is performed on a surface havinglow surface energy (or hydrophobicity) through a mask, only a portion ofthe surface exposed to UV-ozone may selectively have high surface energy(or hydrophilicity). When the substrate on which the UV-ozone processhas been performed is immersed in the ink and is then picked up, sincethe ink selectively soaks into the portion having high surface energy(or hydrophilicity), it is possible to exhibit a desired coffee-ringeffect.

In the inkjet printing method, when the ink is discharged, a volume ofan ink droplet may be 1 μl or less. It is possible to obtain a desiredcoffee-ring effect from the volume of the ink droplet. Further, in theinkjet printing method, a discharging rate may be 100 μm/s to 200 μm/s,but is not limited thereto.

In the forming of a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide or the combinationthereof within the formed pattern, the formed source electrode, anddrain electrode may have a thickness of 5 nm to 50 nm, and the formedsemiconductor channel may have a thickness of 10 nm or less. However, adifference in thickness between the electrodes and the channel regionmay be 2 nm or more. Such a thickness difference may be adjusteddepending on a configuration of a desired transistor, and the adjustmentof the thickness may be achieved by adjusting the coffee-ring effect.

In addition, a distance between the source electrode and the drainelectrode may be 20 μm to 200 μm, but is not limited thereto. Thedistance range may be adjusted by adjusting the coffee-ring effect likethe thickness.

The method of manufacturing a single-process thin-film transistor mayfurther include removing a remaining solvent in the ink after theforming of a source electrode and a drain electrode that are positionedat edges of the pattern and a semiconductor channel positioned betweenthe electrodes by a coffee-ring effect in the ink by using the grapheneoxide, the reduced graphene oxide, or the combination thereof within theformed pattern.

In the removing a remaining solvent in the ink, a heat treatment method,a vacuum drying method, or a combination thereof may be used. It ispossible to increase efficiency in the following reduction step usingthe intense pulsed light through the removing of a remaining solvent. Asa specific example, the temperature in a heat treatment step may be 25°C. to 150° C. However, the present invention is not limited to theabove-mentioned temperature.

As a specific example, the intense pulsed light may have a pulseduration of 1 msec to 500 msec. However, the present invention is notlimited to the above-mentioned pulse duration time.

As another example, the intense pulsed light may have a pulse-off timeof 0.1 msec to 500 msec. However, the present invention is not limitedto the above-mentioned pulse-off time.

As still another example, the intense pulsed light may have energy of 5J/cm² to 200 J/cm². However, the present invention is not limited to theabove-mentioned energy.

The conditions of the intense pulsed light are merely examples, and maybe adjusted depending on a desired effect.

The substrate may include, for example, silicon, glass, an oxide, anitride, or a combination thereof. The substrate may be, for example, asilicon wafer. However, the present invention is not limited to theabove-material.

The intense pulsed light may include, for example, a xenon flash lamp, atriggering/controlling circuit, a capacitor, a reflecting mirror, and anoptical wavelength filter.

A quartz tube may be provided at a lamp housing for the xenon flashlamp, and a water-cooling supply path for cooling the lamp through watercooling may be provided together with a separate cooling device.

The optical wavelength filter may selectively filter a predeterminedwavelength region, and may be changed depending on the kind and size ofparticles and the kind and size of the substrate.

In addition, a vertical distance adjuster, a horizontal substratetransferring device such as a conveyor belt, an auxiliary heating plate,an auxiliary cooling plate, and a beam guide may be provided.

The vertical distance adjuster may adjust a distance between the xenonflash lamp and the substrate, and the horizontal substrate transferringdevice such as the conveyor belt may facilitate a real-time process. Theauxiliary heating plate and/or the auxiliary cooling plate are providedwithin the conveyor belt, so that it is possible to improve efficiencyand quality of a sintering process. The beam guide can accuratelycontrol a path of light, and may be made of, for example, quartz.

The intense pulsed light may be controlled depending on a requiredcondition of a light pulse, and may arbitrarily control, for example, apulse duration time, a pulse-off time, a pulse number, a pulse peakintensity, and an average pulse energy.

The intense pulsed light may illuminate one time or multiple times, andconductivity may be controlled depending on the number of times ofilluminating. For example, the number of times of illuminating of theintense pulsed light may be 1 to 99, and may be 3 to 20 within therange.

It is possible to obtain the reduced graphene oxide by separating oxygenatoms and/or a hydroxyl group existing in the graphene oxide by theilluminating of the intense pulsed light.

As described above, the intense pulsed light may reduce the grapheneoxide within a short time. For this reason, since a chemical fluid suchas a reducing agent is not used during the reducing process, a lowerfilm or an adjacent pattern is not affected, and when the graphene oxideis used to manufacture the electrodes of the thin-film transistor, sincethe channel is not affected, it is possible to implement a favorabletransistor characteristic. Furthermore, it is possible to control adegree of reducing the graphene oxide by controlling the energy of theintense pulsed light.

The reduced graphene oxide may have high electrical conductivity, chargemobility, and transparency similar to the graphene. For example, thereduced graphene oxide may have electrical conductivity of about 0.1S/cm to 15 S/cm and sheet resistance of about 10 kΩ to 100 kΩ at atransparency of about 70% to 90%.

Hereinafter, examples and comparative examples of the present disclosurewill be described. However, the examples described below are merelyexamples of the present disclosure, and the present disclosure is notlimited to the examples.

Example 1 Preparation of Graphene Oxide Solution

25 mg of graphene oxides are obtained by oxidizing 1 g of graphitepowder (Sigma Aldrich) by using 5 g of potassium permanganate.Subsequently, after 2.1 mg of graphene oxides are added to 3 ml ofwater, an ultrasonic wave process is performed on the resultantsolution, and finally, a solution in which the graphene oxide isdispersed is prepared.

Manufacturing of Thin-Film Transistor Through Coffee-Ring Effect

Thereafter, the graphene oxide solution is deposited on the siliconwafer by using the method of selectively controlling the wettability ofthe solution or the inkjet printing method in order to form a patternhaving a width of 50 to 200 μm.

In the method of selectively controlling wettability of the solution, inorder to selectively control the wettability, a hydrophobic surface isfirst formed by self-assembled monolayers on a silicon wafer surface onwhich a silicon oxide with a thickness of 300 nm is layered, usingoctadecyltrichlorosilane.

When a desired pattern is formed on the surface on which theoctadecyltrichlorosilane is formed through the UV-ozone process by usinga mask, a portion of the pattern exposed to the UV-ozone becomeshydrophilic, where a functional group such as a carboxyl (—COOH), ahydroxyl (—OH), or an epoxide (C—O—C) is formed. When the substrate isimmersed in the graphene oxide solution and is picked up, the ink isformed only on the hydrophilic pattern, and the solvent is evaporated.Accordingly, it is possible to obtain a pattern in which a coffee-ringis formed.

In the example, a pattern having a line width of 50 μm to 200 μm and alength of 7500 μm has been formed, but a shape of the pattern is notlimited to the example. As a specific example, FIG. 11 illustratesphotographs of various shapes of patterns other than the line pattern,which are formed by the method of selectively controlling wettability,and data obtained by analyzing thicknesses thereof.

When the inkjet printing method is used, in the example, the pattern isformed under a condition where a discharge volume is 10 pL to 30 pL, adischarging rate is 500 Hz, and a temperature of the substrate is 25° C.

Electrodes and a channel layer are formed using the graphene oxide bythe coffee-ring effect in the pattern. A thickness of the formedelectrodes is 7 nm to 10 nm, and a thickness of the channel layer is 1nm to 3 nm.

Reduction Through Intense Pulsed Light

Thereafter, after the silicon wafer is disposed within a glove box, theintense pulsed light of 30 pulses is illuminated on the graphene oxidepattern for an on-time of 2 msec and for an off-time of 35 msec at anenergy amount of 71 J/cm². By doing this, a reduced graphene oxidethin-film transistor is manufactured.

Thereafter, a connected part of the source and the drain electrodes iscutted by adjusting a channel width using a cutting tip that isself-manufactured.

FIG. 2 illustrates a single-process graphene transistor reduced usingthe intense pulsed light after the coffee-ring effect is induced byselectively controlling the wettability of the solution on the wafer.

Evaluation 1

The reduced graphene oxide pattern according to Example 1 is evaluatedusing X-ray photoelectron spectroscopy (XPS).

FIG. 3 illustrates XPS analyzing results of C1s before and afterprocessing the graphene oxide with the intense pulsed light. It isconfirmed that peaks related to C—O, C═O, and C(O)O are largelydecreased, which means the graphene oxide is reduced.

FIG. 4 is a graph representing electric field effect mobility of thegraphene oxide single-process transistor according to Example 1depending on processing conditions of the intense pulsed light. It isconfirmed that a degree of reducing the graphene oxide by using theintense pulsed light can be controlled.

Evaluation 2

A current characteristic of the thin-film transistor according toExample 1 is evaluated.

FIG. 5 is a graph exhibiting a current characteristic (I_(DS)-V_(DS)) ofthe thin-film transistor according to Example 1.

FIG. 6 is a graph exhibiting transfer characteristic (IDS-VGS)performance of the thin-film transistor manufactured according toExample 1.

From this graph, it can be seen that a gate voltage of the manufacturedthin-film transistor exhibits a transfer characteristic (ambipolartransport) of a typical graphene and is operated as a transistor. (Holeelectric field effect mobility is 0.01 cm²V⁻¹s⁻¹, electron electricfield effect mobility is 0.001 cm²V⁻¹s⁻¹, and an on/off ratio is 3.8)

Evaluation 3

FIG. 7 represents a graph exhibiting a transfer characteristic(IDS-VGS), and the inside of FIG. 7 is the single-process graphenetransistor using the inkjet printing according to Example 1.

From the graph, it can be seen that a typical transfer characteristic(ambipolar transport) of a grapheme with regard to a gate voltage of thethin-film transistor manufactured according to Example 1. Thus, thethin-film transistor of Example 1 is operated as a transistor.

Example 2

A single-process transistor is manufactured using the reduced grapheneoxide solution by the coffee-ring effect.

Preparation of Reduced Graphene Oxide Solution

A hydrazine reducing agent is added to a solution in which the grapheneoxide is dispersed to reduce the graphene oxide. A solution in which 0.1wt % of reduced graphene oxides are dispersed in n-methylpyrrolidone(NMP) is prepared.

Manufacturing of Thin-Film Transistor Through Coffee-Ring Effect

Subsequently, a pattern having a width of 200 μm is formed on thesilicon wafer by using the reduced graphene oxide solution through themethod (the same method as Example 1) of selectively controllingwettability of the solution. At this time, the substrate is heated toincrease the evaporation rate of the solvent, so that it is possible tomaximize the coffee-ring effect.

Evaluation 4

The coffee-ring effect of the patterned solution according to Example 2depending on the temperature of the substrate is evaluated.

FIG. 8 illustrates a single-process transistor of the reduced grapheneoxide (RGO) using the coffee-ring effect according to Example 2. It canbe seen that as the temperature of the substrate is increased, thecoffee-ring effect is maximized.

Evaluation 5

A current characteristic of the thin-film transistor according toExample 2 is evaluated.

FIG. 9 is a graph exhibiting a current characteristic (I_(DS)-V_(DS)) ofthe thin-film transistor manufactured according to Example 2.

FIG. 10 is a graph exhibiting transfer characteristic (IDS-VGS)performance of the thin-film transistor manufactured according toExample 2.

From the graph, it can be seen that the graphene oxide reduced usinghydrazine has p-type transfer characteristic with regard to a gatevoltage of of. Thus, the manufactured thin-film transistor is operatedas a transistor. (Hole electric field effect mobility is 0.05 cm²V⁻¹s⁻¹,on/off ratio is 2.5)

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method of manufacturing a single-processthin-film transistor, comprising: preparing ink including a solution inwhich a graphene oxide, a reduced graphene oxide, or a combinationthereof is dispersed; forming the ink on a substrate in the form of apattern; and forming a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof within the formed pattern.
 2. The method of manufacturing asingle-process thin-film transistor of claim 1, further comprising,after the forming of a source electrode and a drain electrode that arepositioned at edges of the pattern and a semiconductor channelpositioned between the electrodes by a coffee-ring effect in the ink byusing the graphene oxide, the reduced graphene oxide, or the combinationthereof within the formed pattern, reducing the graphene oxide withinthe formed source electrode, drain electrode, and semiconductor channel.3. The method of manufacturing a single-process thin-film transistor ofclaim 2, wherein, in the reducing of the graphene oxide within theformed source electrode, drain electrode, and semiconductor channel,intense pulsed light is used.
 4. The method of manufacturing asingle-process thin-film transistor of claim 3, wherein the intensepulsed light has a pulse duration of 1 msec to 500 msec.
 5. The methodof manufacturing a single-process thin-film transistor of claim 3,wherein the intense pulsed light has a pulse-off time of 0.1 msec to 500msec.
 6. The method of manufacturing a single-process thin-filmtransistor of claim 3, wherein the intense pulsed light has energy of 5J/cm² to 200 J/cm².
 7. The method of manufacturing a single-processthin-film transistor of claim 1, further comprising, in the formedsource electrode, drain electrode, and semiconductor channel, separatingand cutting the source electrode and the drain electrode.
 8. The methodof manufacturing a single-process thin-film transistor of claim 1,wherein, in the preparing ink including a solution in which the grapheneoxide, the reduced graphene oxide, or the combination thereof isdispersed, the solution in which the graphene oxide, the reducedgraphene oxide, or the combination thereof is dispersed includes anorganic solvent, water, or a combination thereof in which the grapheneoxide, the reduced graphene oxide, or the combination thereof isdispersed.
 9. The method of manufacturing a single-process thin-filmtransistor of claim 8, wherein the solution in which the graphene oxide,the reduced graphene oxide, or the combination thereof is dispersedincludes 0.01 wt % to 3 wt % of graphene oxides, the reduced grapheneoxide, or the combination thereof.
 10. The method of manufacturing asingle-process thin-film transistor of claim 8, wherein the organicsolvent is n-methyl pyrrolidone (NMP), dimethylpyrrolidone, ethyleneglycol, acetone, tetrahydrofuran, acetonitrile, dimethylformamide,methanol, ethanol, propanol, dimethyl sulfoxide, chloroform,cyclopentanone, or a combination thereof.
 11. The method ofmanufacturing a single-process thin-film transistor of claim 8, whereinthe organic solvent, the water, or the combination thereof includes afirst solvent and a second solvent, and the second solvent has lowerviscosity and surface tension than those of the first solvent, or hashigher viscosity and surface tension than those of the same.
 12. Themethod of manufacturing a single-process thin-film transistor of claim1, wherein, in the forming the ink on a substrate in the form ofpattern, a method of selectively controlling wettability of thesolution, an inkjet printing method, or a method using a dispenser isused.
 13. The method of manufacturing a single-process thin-filmtransistor of claim 12, wherein, in the inkjet printing method, a volumeof discharged ink is 1 μl or less.
 14. The method of manufacturing asingle-process thin-film transistor of claim 13, wherein, in the inkjetprinting method, a discharge volume is 1 μL or less, a discharging rateis 1 Hz to 1000 Hz, and a temperature of the substrate is 25° C. to 90°C.
 15. The method of manufacturing a single-process thin-film transistorof claim 12, wherein: the substrate includes silicon, glass, an oxide, anitride, a plastic, or a combination thereof.
 16. The method ofmanufacturing a single-process thin-film transistor of claim 12,wherein, in the method of selectively controlling wettability of thesolution, the pattern is formed by allowing the ink to soak into thepattern in which a surface energy is controlled, as a result ofselectively controlling surface energy on the substrate in a regularpattern form.
 17. The method of manufacturing a single-process thin-filmtransistor of claim 1, wherein, in the forming of a source electrode anda drain electrode that are positioned at edges of the pattern and asemiconductor channel positioned between the electrodes by a coffee-ringeffect in the ink by using the graphene oxide, the reduced grapheneoxide, or the combination thereof within the formed pattern, the formedsource electrode and drain electrode have a thickness of 5 nm to 50 nm,and the formed semiconductor channel has a thickness of 10 nm or less.18. The method of manufacturing a single-process thin-film transistor ofclaim 17, wherein a difference between the thickness of source electrodeand drain electrode and the thickness of the semiconductor channel is 2nm or more.
 19. The method of manufacturing a single-process thin-filmtransistor of claim 1, wherein a distance between the source electrodeand the drain electrode is 20 μm to 200 μm.
 20. The method ofmanufacturing a single-process thin-film transistor of claim 1, furthercomprising, after the forming of a source electrode and a drainelectrode that are positioned at edges of the pattern and asemiconductor channel positioned between the electrodes by a coffee-ringeffect in the ink by using the graphene oxide, the reduced grapheneoxide, or the combination thereof within the formed pattern, removingremaining solvent from the ink.
 21. The method of manufacturing asingle-process thin-film transistor of claim 1, wherein the forming asource electrode and a drain electrode that are positioned at edges ofthe pattern and a semiconductor channel positioned between theelectrodes by a coffee-ring effect in the ink by using the grapheneoxide, the reduced graphene oxide, or the combination thereof within theformed pattern includes increasing the coffee-ring effect by heating asubstrate on which the pattern is formed to improve an evaporation rateof a solvent in the ink.